1. Field of the Invention
The present invention relates to articles which have been thermal spray coated with rare-earth oxide powders. The present invention also relates to rare-earth oxide powders for thermal spraying.
2. Prior Art
Because rare-earth oxides are relatively stable at high temperatures, articles which are thermal spray coated with rare-earth oxides to increase the life of the article are being developed for heat-resistant and plasma erosion resistant applications. Examples of such articles include sintering trays used when sintering carbide tools, and components for plasma etching systems that employ halogen gases.
Problems arise because rare-earth oxides such as yttria are generally white in color. When rare-earth oxides are used in trays for sintering carbide tools, constituents of the carbide (e.g., tungsten carbide and carbon) stick to the white surface and appear to contaminate the tray as foreign matter. Moreover, such contamination creates black and white areas on the tray, which results in a non-uniform radiation efficiency during high-temperature sintering. In the sintering of slender, elongated tools such as microdrills in particular, such non-uniformity tends to cause warping.
When rare-earth oxides are used in components for plasma etching chamber using halogen gases, resist decomposition product residues adhere to the component following use, creating areas of brown discoloration. Because such areas invariably receive more attention in the cleaning operation, in spite of being endowed with good plasma erosion resistance and thus inherently greater longevity, the component tends to be excessively cleaned, shortening its useful life.